The long-range goal of this research is to understand the physiologic regulation of proteins encoded by the major histocompatibility complex (MHC). These proteins play key roles in the initiation and regulation of immune responses; elucidating the factors that control their expression will be valuable for understanding not only the normally- functioning immune system but also the processes that cause it to escape normal controls, such as occurs in autoimmune diseases. The focus of this grant period will be on the molecular mechanisms regulating the transcription of genes encoding two murine MCH class II polypeptide chains, A(d-alpha), (a prototype MHC class II gene product) and the invariant chain (I-i), a non- MHC-encoded chain that associates with class II alpha beta dimers intracellularly and may play a role in antigen processing or presentation. A major emphasis of our proposed work in this grant period will be to examine the regulation of these genes in a range of normal cell types since we have evidence that class II genes are differentially regulated by various mediators in different cells and that transformed cell lines do not always respond normally. For the A alpha gene we will continue to characterize cis- and trans-acting factors responsible for constitutive expression in B cells and inducible expression in monocyte/macrophage cells. In addition to continuing our studies of expression of mutant promoter constructs transfected into cell lines, we will also carry out transfection studies in normal macrophages. This will also allow us to investigate transcriptional mechanisms responsible for the inhibition by various mediators of class II expression induced by IFN-gamma or IL-4. We will also generate transgenic mice carrying A(d-alpha) genes with promoter mutations to explore the control of class II expression in a wider range of cell types. For the I(i) gene similar studies will be carried out. Here we will focus on the respective regulatory roles of the enhancer and promoter regions we have recently identified. We will also study cis- and trans-acting elements required for both positive and negative regulation, again using transformed cell lines, normal macrophages, and I(i) transgenic mice. These studies should reveal the mechanisms responsible for the similarities and differences in regulation of the class II alpha and I(i) chains in different cell types and under varying physiological conditions.